This invention relates generally to subsea oil and gas production methods and apparatus and, more particularly, to a split tree cap christmas tree.
The proliferation of rules and regulations for producing and transporting oil, gas, and other products over the years has led to many advances in well equipment and methodology. One object of particular concern in drilling, completion, and workover operations of a subsea well is that at all times there be at least two barriers between the production fluids and the local environment. The standard use of a double barrier prevents contamination in the event of a failure of the first barrier, whether that barrier is a seal, a valve, or some other apparatus.
In a typical well completion with a horizontal tree, it is conventional practice to complete the subsea well with a tubing hanger having a production tubing string suspended therefrom. The tubing hanger and the associated production tubing are run into a subsea horizontal tree on a running assembly usually comprising a tubing hanger running tool and a riser until the tubing hanger is landed and sealed in the horizontal tree. Typically the production tubing includes a downhole safety valve to shut-in production, if necessary. The wellhead carries a blowout preventer (BOP) stack which is connected to a marine riser through which the tubing hanger is run. Often the horizontal tree contains a plug or tree cap that provides a first barrier to production fluids above the tubing hanger and the production tubing in the horizontal christmas tree. A second barrier to the environment is typically provided by a second plug located within the production tubing hanger when the tubing hanger is run or retrieved.
As the well nears completion, or (in a completed well) when a workover or other well service operation is necessary, it is conventional practice to install or retrieve the plug in the tubing hanger to ensure a dual barrier to the ambient environment at all times. The installation of a plug in the tubing hanger becomes necessary, for example, when an operator needs to remove the BOP. However, the setting and/or retrieving of the plug in the tubing hanger requires a separate tripxe2x80x94usually by wireline. Because well drilling and completion operations are very expensive and often based on per hour rig charges, it is desirable to complete and/or service wells with as few downhole trips as possible to reduce rig time. It would be desirable and cost efficient to find a system that would allow well completion and servicing options without setting and retrieving the tubing hanger plug.
There is disclosed a christmas tree to control the production from a subsea oil or gas well. In one embodiment the system includes a tree body having a first flow port and a tree cap; a tubing hanger landed within the tree body; an actuation mandrel landed within the tree body, the actuation mandrel having a flow port; and a flow diverter disposed within the tree cap to divert flow through the flow port. The system may further include a backup flow diverter disposed within the tree cap, the flow diverters including plugs. In some embodiments the plugs are set by wireline.
In one embodiment of the christmas tree the first flow port is a production flow port. This first flow port may be a radial bore extending through the tree body.
In one embodiment the christmas tree includes a second flow port. This second flow port may be an annulus flow port. The annulus flow port may include a first partial bore, a second partial bore, and a channel extending therebetween. The channel may extend substantially longitudinally along the tree body. In one embodiment the first and second partial bores are arranged opposite one another.
In one embodiment the christmas tree further includes an integral production valve. In another embodiment the christmas tree includes a first countersunk area receptive of a production valve assembly.
In one embodiment the christmas tree further includes a second countersunk area receptive of an annulus flow assembly. The annulus flow assembly may attach to external fluid circulation lines. The external fluid circulation lines may include choke or kill lines.
In one embodiment the christmas tree further includes a third flow port. The third flow port provides fluid communication to a downhole safety valve. The third flow port may be receptive of a hydraulic penetrator to establish fluid communication to the downhole safety valve.
In one embodiment the christmas tree further includes a fourth flow port. The fourth flow port may provide for chemical injection into the well.
There is also disclosed a method of controlling production from a subsea oil or gas well, the method including the steps of: installing a side valve tree onto a wellhead, the side valve tree including a tree cap; running a tubing hanger into the wellbore; landing the tubing hanger in the tree body; installing an actuation mandrel with a plurality of plugs set therein; wherein the plurality of plugs are disposed within the tree cap and there are no plugs set in the tubing hanger.
The step of installing a side valve tree onto a wellhead may further include providing a tree bore protector.
According to the disclosed method the tubing hanger may include a production tubing suspended therefrom. The tubing hanger may include an orientation key mating with an orientation sleeve. Therefore, the method may further include the step of orienting the tubing hanger within the tree body.
In one embodiment the method may include the step of locking the tubing hanger within the tree body.
In one embodiment the step of installing an actuation mandrel with a plurality of plugs set therein includes orienting the actuation mandrel. The actuation mandrel may include a plurality of reduced-diameter shoulders and pack-off seals.
In one embodiment the step of installing an actuation mandrel with a plurality of plugs set therein further comprises landing the shoulders and seals within the tree body.
There is also disclosed a method of servicing a subsea oil or gas well with a side-valve christmas tree including the steps of: running an actuation mandrel retrieval tool into the christmas tree; engaging the actuation mandrel retrieval tool with the actuation mandrel; retrieving the actuation mandrel; and retrieving a tubing hanger; wherein there is no step of retrieving any plugs from within the tubing hanger.